Bearing alloy



Patented May 10, 1938 UNITED STATES 2,116,851 BEARING ALLOY Julian G. Ryan, Wood River, Ill., assignor to Shell Development Company, San Francisco, Calif., a corporation of Delaware 4 No Drawing.

Application October 18, 1937,

Serial No. 169,645

4 Claims.

This invention is chiefly concerned with bearing compositions used in internal'combustion engines. It has been recognized that bearings should comprise at least two constituent parts,

5 namely, a soft part to conform to the crankshaft and readjust itself to irregularities in operation and a hard part to support the load and have anti-fractional qualities in order not to seize onto the shaft. These properties have in the past been found in tin base bearing alloys commonly known as babbitt.

In recent years owing to the greater speeds required of automotive engines, the higher oil temperatures produced have caused a softening of the babbitt and in some cases, actual melting due to the eutectic melting point being around 450 F. and the softening point being around 212 F.

Endeavor has therefore been made to develop bearing metals which would have anti-friction properties and have a high enough melting point that the softening temperature would be raised above that of the tin base bearings and at the same time be economical.

Two of the bearing materials which have been produced to meet this requirement are cadmiumsilver and cadmium-silver-copper compositions. Cadmium is the main constituent of these compositions. Cadmium has a melting point of about 650 F. and a Brinell hardness of over 20. Furthermore cadmium has good bonding properties as evidenced by its successful use with zinc in high strength solders.

Silver, when added to the cadmium in relatively small quantities, improves the casting qualities of cadmium by making it less susceptible to oxidation at casting temperatures and by increasing the fluidity. Silver, further, has a markedinfiuence upon the physical characteristics of cad- ;mium by improving grain structure.

A typical cadmium silver bearing allow will have the following composition: cadmium 97.75% and silver 2.25%, the silver being held in solution by the cadmium. The addition of small amounts of copper to the composition has the property of raising the Brinell hardness appreciably. A typical cadmiumsilver-copper composition is as follows: cadmium 98.75%, silver 0.75% and copper 0.50%.

These bearings have, in general, been quite successful. However, in many cases, corrosion of the bearing has taken place. Many theories have been advanced to explain this, and various oil compositions have been devised to reduce this corrsion in the belief that it was entirely due to the lubricant used. However, I have discovered that one of the main causes of becoming corrosive can be traced to the composition of the bearing alloys, and it is the object of this invention to provide substantially non-corrosive bearings for internal combustion engines.

I have found that the corrosion is in part due to galvanic action between the constituents of the bearing material submerged in mineral or hydrocarbon oil. This galvanic action takes place through the intermediary of the lubricating oil. The electrical conductivityof the oil is very slight under normal circumstances, but upon oxidation of the lubricant and the accumulation of small amounts of water in the crankcase of the motor the conductivity is materially increased.

According to my investigation, I have found that in some cases the cadmium-silver bearings after being run in an automobileqinotor for several hours showed pitting of the bearings. Subsequent analysis of the oil failed to show any cadmium particles'in the oil, thus eliminating abrasion of the metal or insuflicient oiliness of the oil as the cause of corrosion. This led to the conclusion that at least part of the corrosion was due to electro-chemical action. This conclusion was further supported by the fact that only the cadmium went intosolution and silver was not found dissolved in oil in conformity with its lower position in the electromotive series. Further experiments were then conducted to establish the electrode potentials between cadmium and silver electrodes placed in a used motor lubricating oil bath. Measured at an oil temperature of 210 F. a potential of .630 volt was established. In order to investigate the effect of electrolyte further, small buttons of polished cadmium with pure silver inserts were exposed to oils under a variety of test conditions. The polished surface was examined under a microscope before and after the tests. The results of thesetests showed that cadmium corrodes easily and that galvanic action accelerates the corrosion. The silver inserts were not attacked. A series of tests with numerous alloys have established that there exists a direct relationship between the rate of corrosion of an alloy and the electric potential between the electrodes made of the alloyed metals, when these electrodes are placed in a lubricating oil electrolyte.

I have found that by alloying a small quantity of a potential depressing substance with the bearing material corrosion may be prevented or at .least substantially reduced. 01 various substances tested in alloys with the cadmium-silver and cadmium-silver-copper bearings I have found that antimony is particularly effective for the purpose desired.

Below are tabulated theresultspbtained using an oil electrolyte at 340 F. 7

. Equilibrium fl gggg Composition oianode potential volts Silver i" v 545 8ilver Oadmium--0. antimonybywt--. 470 Silver Cadmium+2. antimony bywt... 410 Silver Cadmium- 5. ,antimonybywt--. j 896 From .the above "it will be seen that cadmium alone gave an equilibrium potential of 545 milli- 'volts.- Corrosion of the cadmium wasapparent' after about 15 minutes in the test cell. Durinl this time the surface of the cadmium electrode changed considerably. polishedflnish but later showed a coarse grain structure. The addition of antimony to cadmium reduced the potential and corrosion with the result that the cadmium-antimony electrodes after an hour, had a very fine grained finish and showed only slight corrosion. Microscopic examination showed that the crystal structure of the-metal was changed by the presence of the antimony; This is probably also a factor in reducing corrosion.

Further tests were made, using a silver cathode and an anode of standard cadmium-silver-copperbearing metal and anodes of the same with small amounts. of antimony added. The results of these tests are tabulated below using the same oil at 340F. I

' I Equilibrium 333333" Composition -01 anode mama X Silver Commu'cial mdminm-silver-copper. 625 Silver Commercial eadmium-silvef-copper O 406 +0.l% antimony by wt. Bilver Commsciaicsdmium-silver-cepper 1466 +03% antimony by wt. f

To obtain further information regarding the addition of antimonyto bearing alloys the following test was made: Small pieces of the same material-as was used for the anodes in the above test were machined into the form oi cylindrical At first it had a bright I 4%, antimony 0.1%

slugs weighing 8 grams each, carefully polished and washed with solvent. Each specimen was then placed in a test tube containing a measured amount of a used lubricating oil. The test tubes and contents were each kept at a temperature of 340- F., air was continually bubbled through the. oil to simulate actual operating conditions. At the end of a period of sixteen hours the slugs were removed and after careful washing and From. the above it appears conclusively that both by equilibrium potential tests and actual corrosion tests of the bearing metal that antimony has the effect of reducing the corrosion of bearing when added in small quantities. Antimony hardens the alloy and for this purpose copper has been in the past added to cadmiumsilver bearings. It is therefore possible to replace 7 the copper with antimony which will serve both to harden the alloy and reduce corrosion; While I have shown only tests using specific amounts of antimony, the conclusion snust bedrawn that amounts betweenthe examples will 'be beneficial for the purpose intended and that v myself tothe exact proportions given. s

I do not intendto limit Iclaim as'rnydnventioni '1. A bearing metal consisting of siiver 1% to 2'. A bearing 7 p 4%, antimony 0.1% toCBiG. and-the remainder cadmium. jii' 3. A bearing metal 4%,,antimony 0.1% to 0.2%., and the remainder cadmium;

. 4. A bearingmetal of filver let to metal maintainer-1% tomm, and the remainder consisting of amt-1% to 4%, antimony 0.1%, and the remainder cadmium.

0. arm. 

